The present invention relates to a finisher having a stapler for stapling a stack of paper sheets transported to a two-sided copy tray incorporated in, for example, a copier, facsimile machine or printer or to a bin of a sorter. More particularly, the present invention is concerned with a finisher having a paper positioning device capable of positioning paper sheets positively and accurately with no regard to the elasticity of the sheets.
A finisher for positioning paper sheets sequentially distributed to a two-sided copy tray or any of multiple bins of a sorter and stapling a stack of such paper sheets by a stapler has been proposed in various forms in the past. A prerequisite with this type of finisher is that a stack of paper sheets driven out onto the tray or the bin be positioned first. For this purpose, this type of finisher has a paper positioning device. A paper positioning device has customarily been implemented with a jogger member which jogs toward and away from a bin fence for thereby positioning paper sheets. The jogger member is shiftable to a position matching a particular size of paper sheets used. However, difficulty has been experienced in positioning paper sheets surely and accurately with no regard to the kind and the degree of elasticity of paper sheets. On the other hand, a paper stack so positioned on the tray or the bin has to be moved to a stapling position. To this end, it is a common practice to use a mechanism which moves a stapler toward the tray or the bin or a mechanism which moves the tray or the bin toward a stapler. This kind of scheme, however, increases the overall scale of the finisher. Moveover, since the mechanism, whether it moves a stapler or a bin, does not directly handle a paper stack, it is difficult to maintain the stapling position constant. To eliminate this problem, a finisher of the type described is provided with a paper pulling device for pulling a paper stack to the stapling position of a stapler. Specifically, a paper pulling device has a pair of chucks for chucking a paper stack and moves them between a chucking position and a stapling position in the horizontal direction. The coactive chucks are rotatable toward each other to grip a paper stack and away from each other to release it. However, paper pulling devices heretofore proposed have some problems left unsolved regarding the applicability thereof to a finisher, as will be described specifically later.